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Re: Shouldn't this script terminate on ^C?

From: Nikolaus Schulz
Subject: Re: Shouldn't this script terminate on ^C?
Date: Wed, 20 Feb 2013 13:52:27 +0100
User-agent: Mutt/1.5.20 (2009-06-14)

On Tue, Feb 19, 2013 at 03:17:55PM -0500, Chet Ramey wrote:
> On 2/19/13 1:42 PM, Nikolaus Schulz wrote:
> > Please consider this bash script:
> > 
> >   : | while true; do sleep 1; done
> >   echo "After loop"
> > 
> > If I hit ^C while it runs, shouln't it terminate?


> You're not going to find anything in Posix.  This was discussed
> exhaustively two years ago, in a thread starting with
> http://lists.gnu.org/archive/html/bug-bash/2011-02/msg00050.html


> It turns out there were some races in bash's implementation of the
> intended behavior.  Those have been fixed, and the current bash-4.3
> development versions exit the script before the echo.

Thanks for the link. So, the behaviour above is a bug triggered by the :
exiting before the signal arrives, and bash assuming that : handled the

Note that current bash only seems to check the first command in a pipeline for
its signal handling, see the following snippet:

  loop()  { while true; do sleep 1; done; } 
  dies()  { loop; }
  exits() { trap 'exit 0' INT; loop; }

  # This sequence writes "Alive" twice.
  :     | dies ; echo Alive
  exits | dies ; echo Alive
  # bash exits here.
  dies  | exits; echo Alive
  echo "Script completed."

The development version of bash works as expected.


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